A backlight is a light emitting component installed behind an LCD. A backlight is used to improve legibility of a small-sized display. It is also used to emit light from a computer display or an LCD television as does a CRT.
A backlight has been regarded as a low-tech component for a while because manufacturing a backlight was relatively easy compared with other LCD components used for notebook computers or monitors. The significance of a backlight has been gradually increased, however; currently, it is one of key components affecting growth of LCD market. A backlight in good quality can dramatically improve image quality and color reproducibility. Therefore, it may be said that backlights hold the key to the advancement of LCD-TVs. Types of backlights include cold cathode fluorescent lamp (CCFL), external electrode fluorescent lamp (EEFL), light emitting diode (LED), and flat fluorescent lamp (FFL).
FIG. 1 is a cross sectional view of an edge-type backlight unit according to a prior art. In an edge-type backlight unit according to a prior art, light emitted from a light source 110 propagates through a light guide plate 140 making total reflection. The critical angle for total reflection is determined by the ratio of a refractive index of a propagation medium to that of air layer, which can be derived from Snell's law. A ray of light striking a medium boundary at an angle below the critical angle propagates with a minimal loss of energy unless the light hits a structure which makes the light reflect more than the critical angle. In case of a printed light guide plate, diffusion and transmission of light are made to occur through a white dot pattern 130.